Tag Archives: evolution

Book Review: Daniel Lieberman’s The Story of the Human Body


In The Story of the Human Body Daniel Lieberman builds a strong case that making fully informed decisions about diet and lifestyle is only possible through the lens of evolutionary history. If you want to know where your body comes from, you need to understand its evolutionary history. Why do humans stand and walk on two legs? Why are we weak compared to other primates of comparable size? Why are our legs and feet shaped the way they are, with springy tendons and arched feet? Why does our spine have a special S-curve? The answer to these questions lies in the the evolutionary history of our species.

Now ask, why do people in modern societies suffer from “diseases of affluence” like obesity, type-2 diabetes, tooth decay, metabolic syndrome, flat feet, nearsightedness, lower back pain, and sleep disorders? Daniel Lieberman argues that these questions can only be fully answered by understanding the evolutionary history of our species. Lieberman argues these diseases are examples of “mismatch diseases” i.e. a disease that is primarily caused by our bodies not being sufficiently adapted to novel gene-environment contexts. We know they’re mismatch diseases primarily because they used to be rare, are largely preventable, and are almost unheard of in hunter-gatherer populations.

Lieberman argues that all of these diseases are in some sense a result of cultural evolution speeding ahead of natural evolution with the result that have humans manufactured a psychologically comfy and satisfying environment that is paradoxically unhealthy without fundamentally affecting our reproductive fitness. Lieberman calls this this paradoxical unhealthiness “dysevolution”. It turns out that surrounding ourselves with unlimited sources of cheap junk food is a bad idea because humans are genetically wired to crave food with dense amounts of fat, sugar, starch, and salt.

Lieberman is no luddite, and certainly doesn’t advocate a return to the caves and giving up on modern science and technology. His position is more nuanced than many of the extreme black and white positions out there, as befitting the complexity of gene-environment interaction. In many senses, the agricultural and industrial revolutions have propelled humans to new heights of health and longevity, with modern science curing diseases and fixing people better than ever before. At the same time, we are living longer but spending many of those years suffering from chronic, preventable diseases. The paradox of the modern world is reduced mortality but greater morbidity i.e. living longer, but spending more of those extra years with an illness of some sort. Lieberman argues that too often the incentives of modern medicine aim at fixing symptoms but not the underlying structural causes: the toxically comfortable environments we built for ourselves.


Filed under Books, Psychology

Quote for the Day – The Evolutionary Logic of Love

As Steven Pinker observes, the logic of loyalty is particularly clear in the domain of romantic relationships: You’re a great catch, but there is bound to be someone out there who’s got everything you’ve got plus a little more. Knowing that your partner might someday meet such a person, you’d be reassured by the knowledge that your partner isn’t going to leave you as soon as something better comes along. This would make you much more willing to settle down with your partner and start a family–a high-stakes cooperative endeavor if ever there was one. It’s wonderful that your partner fully appreciates your many marketable qualities, but that may not be enough to keep you together. What you really want is for your partner to have a deep, unshakable desire to be with you and you alone. In short, you want your partner to love you, to want you not only for your wonderful qualities but just because you’re you. Only love provides the kind of loyalty you need in order to take the parenting plunge. Thus, love appears to be more than just an intense form of caring. It’s a highly specialized piece of psychological machinery, an emotional straitjacket that enables cooperative parenting by assuring our parenting partners that they won’t be abandoned.

~Joshua Greene, Moral Tribes: Emotion, Reason, and the Gap Between Us and Them (2013), p. 42

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Book notice: Stephen J. Gould’s The Panda’s Thumb

A used copy of Stephen J. Gould’s book The Panda’s Thumb (1980) has been sitting on my shelf for a while, and I’m kicking myself for not reading it sooner. What a delightful little book of science essays! Each essay is an edited version of one of his monthly columns at Natural History magazine. Subsequently, the essays are intelligible to the general intelligent reader, but Gould does not thereby sacrifice an appreciation for hard facts and subtle reasoning. Gould makes science come alive with his anecdotes, wry humor, and gentle argumentation about topics ranging from the panda’s thumb to hopeful monsters and everything in between. Nothing is too big or small for Gould to think worthy of writing about. All in all, I highly recommend this book for any student of biology or lover of science.

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Quote for the Day – Is Evolutionary Biology Inherently Sexist? No, says Sarah Hrdy

Evolutionary biology, and its offspring, sociobiology, are not inherently sexist. The proportion of “sexists” among their proponents is probably no greater than the proportion among scientists generally. To be sure, contemporary analyses of mammalian breeding systems can cause even a committed Darwinian like myself to contemplate her gender with foreboding. Yet, it is all too easy to forget, while quaking, that sociobiology, if read as a prescription for life rather than a description of the way some creatures behave, makes it seem bad luck to be born either sex.

~Sarah Blaffer Hrdy, The Woman That Never Evolved, p. 14

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Quote for the Day – Evolutionary Biology, Social Darwinism, and Feminism

Social Darwinism has, almost indelibly, tainted most people’s understanding of evolutionary theory-certainly as it applies to human beings. Yet social Darwinism differs from Darwinism-without-adjectives in one all-important way, and ignoring this distinction has been one of the most unfortunate and long-lived mistakes of science journalism. Darwinism proper is devoted to analyzing all the diverse forms of life according to the theory of natural selection. Darwinists describe competition between unequal individuals, but they place no value judgment on either the competition or its outcome. Natural-selection theory provides a powerful way to understand the subordination of one individual, or group of individuals, by another, but it in no way attempts to condone (or condemn) subordination.

By contrast, social Darwinists attempt to justify social inequality. Social Darwinism explicitly assumes that competition leads to “improvement” of the species; the mechanism of improvement is the unequal survival of individuals and their offspring. Applying this theory to the human condition, social Darwinists hold that those individuals who win the competition, who survive and thrive, must necessarily be the “best.” Social inequalities between the sexes, or between classes or races, represent the operation of natural selection and therefore should not be tampered with, since such tampering would impede the progress of the species. It is this latter brand of Darwinism that became popularly associated with evolutionary biology. The association is incorrect, but it helps to explain why feminists have steadfastly resisted biological perspectives.

~Sarah Blaffer Hrdy, The Woman That Never Evolved, p. 12-13

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Quote for the Day – Sarah Blaffer Hrdy: We Are Composites

I was driven to understand my past. For we are not ready-made out of somebody’s rib. We are composites of many different legacies, put together from leftovers in an evolutionary process that has been going on for billions of years. Even the endorphins that made my labor pains tolerable came from molecules that humans still share with earthworms.

~Sarah Blaffer Hrdy, Mother Nature: A History of Mothers, Infants, and Natural Selection

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New paper completed: “A Genealogical Defense of Normative Nihilism” ; feedback welcome

“One ought not torture for fun.” Few would challenge this norm. But why? A common answer is that norms are “prescriptive”, telling us how we should act. Moreover, such norms are regarded as “authoritative”, possessed with a “binding force” that “governs” rational beings. What is the nature of this “normative force” and its “binding power”? Philosophers sometimes talk about different strengths of normative force, invoking the traditional distinction between hypothetical and categorical norms.

Hypothetical norms are “weakly” binding and exemplified by social conventions e.g. “One ought to use the small fork for salads.” Few people would consider it wrong to use the big fork because this norm only “binds us”if we want to impress high society. The force of hypothetical normativity is thus tied to our individual desires; if my desire to rebel against high society is stronger than my desire to fit in, I am hypothetically bound to not use the small fork.

In contrast, categorical norms such as “One ought not torture for fun” are “strongly” binding in the sense of not being conditional on anyone’s actual or ideal desires. If a psychopath desires to torture others for fun, they are nevertheless obligated to not torture for fun. Unlike their hypothetical cousins, categorical norms are considered “objectively prescriptive” (Mackie, 1977), enjoying what Aquinas calls “the binding force which is proper to a law”.

Suppose categorical force is merely a dressed up version of hypothetical force. How could we tell otherwise? The existence of a “binding” categorical force is not an obvious or trivial truth, nor detectable by any scientific instrument (that I know of). On these grounds alone, a skeptic might propose the “bindingness” of categorical force is merely hypothetical force masquerading as something stronger,a remnant of an old brain disposed for religiosity and magical thinking.

The normative realist claims categoricity is felt as forceful because it really is forceful in virtue of the binding power of “irreducible” normative facts. In contrast, the normative nihilist claims the bindingness of normativity derives its “force”merely from biological and cultural values, but there is no ultimate fact about which values are “better” than any other because, from the physicalist point of view, the universe is cold, uncaring, and ultimately valueless. Nietzsche’s statement of the worldview driving normative nihilism is definitive: “Whatever has value in our world now does not have value in itself, according to its nature—nature is always value-less, but has been given value at some time” (Nietzsche, 1974, p. 242, emphasis added). Nietzsche offers a “physiological” explanation of the source of normativity by tracing the concrete human origins of the concept of categoricity, explaining away the phenomenology of “binding” normative authority as a figment of an over-active brain.

Critics accuse normative nihilists of being either incoherent or hypocritical because in defending the view they “help themselves” to normative concepts, and thus undermine their own attempts at making a meaningful, rational, or intelligible claim. Thus, normativists are doubtful genealogical stories have any revisionary implications for our normative concepts. And even if they did, normativists pull out their trump card tu quoque argument: even if an evolutionary critique of moral norms were successful, it would thereby “prove too much” by casting doubt on all norms, including the epistemic norms that rationally “bind” nihilists to avoid saying “This genealogy both happened and did not happen.” Skeptics have dealt with this “global” challenge creatively, but few have opted to bite the bullet on epistemic nihilism for fear of committing “intellectual suicide” (Sorensen, 2013).Philosophers are by professional reputation defenders of epistemic authority and—not surprisingly—tend to dismiss the prospect of Global Normative Nihilism(GNN)as absurd or self-defeating.

My central thesis is once we distinguish between hypothetical and categorical strengths of epistemic authority the charge of self-defeat rings hollows, for the following reason. If epistemic norms only “bind” us hypothetically with respect to our contingently held desires and/or values, pointing out epistemic nihilists have “binding” hypothetical reasons to avoid holding contradictory beliefs is consistent with the nihilistic claim that acting in accord with epistemic norms is not good in-itself, because nature is valueless. The psychological inevitability of normal humans to feel “bound”by epistemic norms does not entail we are categorically bound to follow them. Naturalists have no beef with hypothetical forms of “binding force” because this locution is understood as a conceptual metaphor. The naturalistic worldview driving normative nihilism predicts that organisms project hypothetically binding values on a valueless world.

Read the full paper HERE: Williams – Genealogy QP 2 version 1.7 8-16-2013


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Defending Paleo, a Response to Marlene Zuk’s critique of “Paleofantasy”

I’ve been meaning to write a post defending the evolutionary logic of the so-called “Paleo diet” for awhile, but it wasn’t until I read Marlene Zuk’s article in the Chronicle “Misguided Nostalgia for Our Paleo Past” that I really felt motivated to do so. Normally my approach to engaging with another thinker is to write in essay format, but my problems with Zuk’s article are numerous enough to warrant a point-by-point reply. Here goes!

 These scientists are looking for signs of changes in the genes that allow us to consume dairy products past the age of weaning, when all other mammals lose the ability to digest lactose, the sugar present in milk. [emphasis added]

Right away Zuk trades off a sneaky ambiguity in her use of “us”. The way she phrases it suggests she means “all humans”, when in fact the majority of humans (especially in Asiatic populations) are lactase-nonpersistent, which is defined as being unable to completely digest lactose. Wikipedia links to a 2003 paper in Annual Review of Genetics that starts off saying “In most mammals…lactase activity declines after the weaning phase, and this is also the case in the majority of humans throughout the world who are described as lactase nonpersistent.” So if the science says that only 25% of adult humans can fully digest milk, it’s clearly misleading to talk about “our” ability to consume dairy when by “our” she could only mean a minority of humans. And if this is the case, is it so unreasonable to use “evolutionary logic” to guide dietary decision making? You don’t need to know about evolution to not drink milk if you are lactose intolerant but as the phrase goes, nothing in biology (or nutrition) makes sense except in the light of evolution.

But in some groups of humans, particularly those from Northern Europe and parts of Africa, lactase—the enzyme that breaks down lactose—lingers throughout life, allowing them to take advantage of a previously unusable food source.

Ok, so she acknowledges later that it’s “some groups”. But why be so misleading in the first place?

The details of their experiences, of course, are lost forever. But the signature of what they were able to eat and drink, and how their diet differed from that of their—our—ancestors, is forever recorded in their DNA.

And it’s also recorded in archaeological sites and food dumps. Archaeologists can learn a lot about dietary habits of our ancient ancestors based on the remains of food in the garbage.

Other than simple curiosity about our ancestors, why do we care whether an adult from 4,000 years ago could drink milk without getting a stomachache? The answer is that these samples are revolutionizing our ideas about the speed at which our evolution has occurred, and this knowledge, in turn, has made us question the idea that we are stuck with ancient genes, and ancient bodies, in a modern environment. We can use this ancient DNA to show that we are not shackled by it.

There is a crucial difference between the notion that we are stuck with ancient bodies and the notion that we are highly constrained by our ancient bodies. I don’t know of any serious Paleo enthusiast who thinks in these absolutist terms of being “shackled” to the past. Zuk has a journalistic tendency to only engage with extreme caricatures of the position she’s attacking. We could distinguish between strong and weak versions of the Paleo hypothesis, but Zuk only attacks the absurd idea that evolution has “stopped”. But surely it’s possible to accept the idea both that evolution can in some cases work faster than was once thought and there are some things that we should minimize in our diets (like refined sugar). There is nothing incompatible with thinking that humans are adapting to some aspects of the modern environment but that the adaption isn’t complete enough to warrant throwing caution to the wind and treating, say, a fillet of salmon as nutritionally equivalent to chocolate chip cookies because, hey, perhaps we will deventually develop “cookie tolerance”. It happened with milk right? So why not cookies? Or Bob Evans’ Stacked & Stuffed Strawberry Banana Cream Hotcakes?

The absurdity of thinking humans will be adapting to Bob Evan’s Hotcakes anytime soon is highlighted by the obvious empirical observation that people with diets featuring heavily in such foods suffer from more health problems such as obesity, type-II diabetes, metabolic syndrome, cardiovascular disease, etc. But wait you say! What if Hotcake eaters out-breed the health nuts? Wouldn’t that provide pressure to adapt to Bob Evan’s Hotcakes? But it’s possible they would be reproductively successful in spite of their bad diet and not because of it.

That assumption makes us feel that humans, who have gone from savanna to asphalt in a mere few thousand years, must be caught out by the pace of modern life, when we’d be much better suited to something more familiar in our history. We’re fat and unfit, we have high blood pressure, and we suffer from ailments that we suspect our ancestors never worried about, like post-traumatic-stress disorder and AIDS.

Zuk conveniently forgets to mention the primary “diseases of affluence” such as  type 2 diabetes, metabolic syndrome, asthma, coronary heart disease, cerebrovascular disease (stroke), peripheral vascular disease, cancer, alcoholism, gout, and some types of allergies. Gary Taubes has brilliantly chronicled the history of hunter-gatherer peoples being introduced to the “Western diet” of cheap processed flour and sugar in bulk. This shift in diet is inevitably correlated with rises in the diseases of affluence. A study even came out recently saying “Mesolithic hunter-gatherers living on a meat-dominated, grain-free diet had much healthier mouths that we have today, with almost no cavities and gum disease-associated bacteria, a genetic study of ancient dental plaque has revealed.” If you look at the dental health of the Royal Families’ of the ancient South/Central American empires, they inevitably had rotten teeth from being able to afford to eat sweet corn snacks all day. Guess what product makes up 90% of the food in the supermarket aisles? Corn!

That’s why the prescription for good health may be as simple as asking, “What would a cave woman do?”

This is a laughably simplistic caricature of how Paleo people approach their diet. Sure, like pretty much any human activity, there will always be people who get excited about lifestyle change and take it to the extremes, but the Paleo diet isn’t all or nothing. As others have said, it’s ideally a template to build a diet around not a sacred covenant to never eat sugar or carbs again. It’s a heuristic not a holy grail. If all you did was minimize the foods Paleo people discourage rather than never ever eat them you would do wonders for your health. If all you do is stop drinking sugary beverages and try to minimize your consumption of sweets, that would still be a net positive.

“Our bodies evolved over hundreds of thousands of years, and they’re perfectly suited to the life we led for 99 percent of that time living in small hunting and gathering bands,” writes a commenter on the New York Times health blog Well.

You know you are dealing with a strawman when you have to get your opposition quotes from the comment sections of health blogs. Why not quote from, you know, actual scientists who have written books on the Paleo and low-carb diet?

Some of our nostalgia for a simpler past is just the same old amnesia that every generation has about the good old days.

Instead of engaging with the scientific evidence piling up against the heavy consumption of sugar and refined carbs, Zuk proceeds to psychologize her opponents. This often happens in debates that are based more on ideology than science. Unfortunately, Zuk’s article is a fluff-piece heavy on ideology but light on science, which is ironic as Zuk herself is a scientist.

Now we worry about our kids as “digital natives,” who grow up surrounded by electronics and can’t settle their brains sufficiently to concentrate on walking the dog without simultaneously texting and listening to their iPods.

This article started has an attempt to engage with people who promote a Paleo diet  but now she is also lumping these people in with those who worry about technology in general. This is a poor argumentative strategy because obviously providing a critique of Luddism is irrelevant to concerns about nutrition and health.

To think of ourselves as misfits in our own time and of our own making flatly contradicts what we now understand about the way evolution works.

This is another conflation between the dietary lifestyle of Paleo versus the broader Luddite lifestyle of commenters on health blogs.

Given this whiplash-inducing rate of recent change, it’s reasonable to conclude that we aren’t suited to our modern lives, and that our health, our family lives, and perhaps our sanity would all be improved if we could live the way early humans did. [emphasis added]

This is another extreme caricature. Paleo is the idea that our lives would be improved if we ate like early humans, not lived. Obviously these are two different things. One is a complete lifestyle reversion based on fantasy, the other is a sensible approach to building dietary templates.

Newspaper articles, morning TV, dozens of books, and self-help advocates promoting slow-food or no-cook diets, barefoot running, sleeping with our infants, and other measures large and small claim that it would be more natural, and healthier, to live more like our ancestors. [emphasis added]

I just had to comment: Zuk is woefully out-of-step with contemporary scientific research on the emotional benefits of co-sleeping. Zuk should read The Science of Parenting and get her facts straight.

We cannot assume that evolution has stopped for humans, or that it can take place only ploddingly, with tiny steps over hundreds of thousands of years. In just the last few years we have added the ability to function at high altitudes and resistance to malaria to the list of rapidly evolved human characteristics, and the stage is set for many more.

Nothing Zuk says here is incompatible with the sensible thought that it’s bad for your health to eat too much sugar, heavily processed enriched flour products, or high-fructose corn syrup. Zuk seems to suggest that because the “stage is set” for future adaptations, we can be justified in eating whatever we want because, hey, maybe it will one day be good for us! This would of course be an absurd way to make dietary decisions.

The paleofantasy is a fantasy in part because it supposes that we humans, or at least our protohuman forebears, were at some point perfectly adapted to our environments.

I don’t know any serious thinker who understands evolution who thinks we were at some point “perfectly” adapted. Perhaps commenters on blogs might think such things, but should Zuk pat herself on the back for successful rebutting an incredibly naive and simplistic hypothesis held only by laypersons?

These often conflicting needs mean automatic trade-offs in every system, so that each may be good enough but is rarely if ever perfect.

It’s laughable that Zuk is lecturing Paleo folks about the notion of “trade-offs” because the whole logic of Paleo is based on the idea that there is a trade-off for having a undiscriminating sweet-tooth that cannot stop once started versus a “smarter” sweet-tooth that is more computationally costly but would use more strategic planning in consuming sugar.

Did we really spend hundreds of thousands of years in stasis, perfectly adapted to our environments?

Not surprised to see another strawman.

For that matter, it might be nice to be unicellular: After all, cancer arises because our differentiated tissues run amok. Single cells don’t get cancer.

It must be convenient to have the luxury of only attacking the most absurd versions of your opponents ideas.

 How do we know what we do about the rate at which evolution occurs? If lactose tolerance can become established in a population over just a handful of generations, what about an ability to digest and thrive on refined grains, the bugaboo of the paleo diet?

This is a specious line of reasoning. First of all, lactose tolerance has yet to be established in something like 75% of the human population. Second of all, we can determine the proximal chain of biological causes that explains why eating milk if you are lactose intolerant has an overall negative health effect. And it just so happens that it’s fairly easy to determine a proximal chain of causes that links excessive grain consumption with increased blood glucose levels, which has been scientifically linked to a range of health problems such as arterial inflammation, insulin resistance, and metabolic syndrome. If we followed Zuk’s logic, we should tell people who are lactose intolerance that it’s ok to eat milk because maybe a mutation will happen in the future that will make it healthier. If we already know the proximal mechanisms for why eating grains is bad, then we should continue avoiding them until something in the causal chain changes. But right now the evidence suggests that spiking your glucose levels with excessive grain consumption is not healthy and speculation about mutations in the future is irrelevant. Until I see concrete evidence that the proximal mechanisms have changed enough to nullify all these known effects, I will continue to restrict my intake of refined carbs the best I can. 

Ok, that’s enough. I think I’ve made my point.


Filed under Psychology, Random

Why Us and Not Them? A Review of Sarah Hrdy’s Mothers and Others

“Thou hast no sense. You French people love your own children; but we love all the children of our tribe.” ~Naskapi tribesman

Sarah Hrdy has done the field of evolutionary psychology an inestimable service by writing Mothers and Others: The Evolutionary Origins of Mutual Understanding (2009). First and foremost, Hrdy has contributed to the advancement of a burgeoning field by bringing together a large and diverse assortment of cutting-edge empirical work in one volume. Second, Hrdy’s deep familiarity with recent work in primatology and cross-cultural anthropology provides a helpful constraint on evolutionary speculations about the human “Environment of Evolutionary Adaptedness” (EEA). Insofar as Hrdy’s book can be seen as a plea for sociobiology to go beyond weakly substantiated speculation about our ancestral way of life, it deserves attention by anyone interested in the origins of human cognition.

The first chapter kicks off with a provocative thought experiment. Hrdy points out that we take it for granted just how well humans get along when stuffed on an airplane with three hundred cranky strangers.  But imagine the same airplane crammed shoulder-to-shoulder with chimpanzees. The inevitable bloody mayhem stands in stark contrast to the overt politeness usually governing human strangers. Hrdy now asks the central question of the book: Why us and not them?  That is, why do humans get along so well with each other but chimps don’t?  Hrdy says “The goal of this book will be to explain the early origins of the mutual understanding, giving impulses, mind reading, and other hypersocial tendencies that make [riding airplanes] possible” (p. 4).

Hrdy catalogues several traditional answers where the difference between humans and chimps has to do with our big brainy intelligence. After arguing the fossil record paints a different story,  Hrdy chastises such overly “intellectualist” stories for putting the cart before the horse and instead favors a hypothesis recently argued by Michael Tomasello (Herrmann et al., 2007; 1999): “The crucial difference between human cognition and that of other species is the ability to participate with others in collaborative activities with shared goals and intentions” (p. 9). Why are humans so “ultra-social” compared to chimps? It obviously won’t do to point to the existence of special human capacities like our ready disposition for empathy because that only pushes the question back further: why do humans have such capacities but chimps don’t? Given that natural selection is blind to possible future benefits, there must have been some “initial payoff” for developing such social-cognitive competencies. Clearly we will need to give an “ultimate” evolutionary explanation for the origin of our uniquely human social-cognitive competencies that outlines a plausible fitness payoff.

In the second chapter, Hrdy reviews contemporary evolutionary accounts of our social-cognitive capacities and finds them lacking. A popular theory is to claim that increased intersubjectivity would have been adaptive for a  group of social primates, particularly with respect to “intergroup conflict” (Choi & Bowles, 2007). However, Hrdy asks “How much sense would it have made for our Pleistocene ancestors eking out a living in the woodland and savannas of tropical Africa to fight with neighboring groups rather than just moving?” (p.19)[1] Moreover, Hrdy is skeptical of these hypotheses for a more general reason. She asks,

If intersubjectivity was so useful for maintaining cohesive social groups, defending one’s in-group from violent neighbors, or wiping out competitors, why didn’t other social primates (those ‘demonic neighbor-stalking chimpanzees in particular) evolve such gifts as well? (p. 37)

Hrdy applies a similar logic to other evolutionary accounts such as the Machiavellian Intelligence hypothesis or the hypothesis that humans are special because we have mirror neurons. For Hrdy, most hypotheses on the table either fail to answer the question, “Why us and not them?” or they rely on empirically false claims about the abilities of chimpanzees (e.g. the false claim that chimp infants cannot imitate or follow eye-gaze, see p. 58). Hrdy’s ultimate diagnosis of all these false starts is that they mistakenly used the chimpanzee model as a basis for theorizing about our human ancestors. Hrdy’s prescription is to turn to recent developments in primatology and cross-cultural anthropology to study how human childcare in extant hunter-gatherer societies works, and from there find an appropriate primate model to make inferences about the EEA.

The third chapter in a nutshell is Hrdy’s defense of the old expression “It takes a village to raise a child”. Indeed, Hrdy’s overall answer to the central motif of the book is that the  selection pressure for human competence in social cognition arose due to novel rearing conditions approximately 1.8 million years ago where youngsters depended on more people than just their parents for care. Hrydy proposes that these “alloparents” like sisters, aunts, grandmothers, and even extended exchange networks involving non-paternal males were the crucial link in the evolutionary story. If a child’s survival in the EEA would have been affected by the availability of alloparental care, then there could have been selection pressure for infants to develop the mental resources to decode the mental states of others in order to illicit extra-parental help. As Hrdy puts it, “the need for alloparental succor transformed the selection pressures that shaped our species, and in doing so altered the way infants developed and then the way humans evolved” (p. 67). Although she acknowledges a possible role for intergroup competition in shaping our prosocial attitudes (p. 20), Hrdy believes many researchers have overlooked the crucial importance of child-rearing and have not sufficiently thought about the difficulty of ensuring the survival of helpless, slow-maturing children in the wild.

To support her hypothesis, Hrdy turns to primatology data (some of which she collected herself) to examine patterns of mother-child care in Great Apes. The most salient finding is that Great Ape mothers under no circumstances ever hand over the infants to another caretaker (even sisters eager to practice their parenting skills). This stands in sharp contrast to modern hunter-gatherer societies where “mothers trust others and allow them to take their infants shortly after birth” (p. 78), a form of child-rearing known as “cooperative breeding”. According to Hrdy, humans are not the only cooperative breeders, a distinction also shared by a family of New World monkeys called the callitrichids, of whom the marmosets are a representative example.[2]  Although humans are cognitively similar to chimps in many ways, it is these “dumber” yet socially sophisticated New World monkeys that may provide the best primate model for reconstructing the EEA in virtue of their shared emotional proclivity for prosociality and cooperative breeding (Not to mention the sociality seen in bonobos, who are genetically equa-distant from humans as chimps).

In the fourth chapter, Hrdy takes up the popular 20th century framework of “attachment theory” and updates it in light of recent developments in the study of alloparenting in human societies. John Bowlby, the founder of attachment theory, famously modeled the mother-child attachment relationship on the iconic notion that the mother and child were inseparable, just like chimp mother-infant relationships. Reviewing both old and new data, Hrdy concludes that modern research on attachment formation overwhelmingly suggests that the development of healthy social attachments depends crucially on forming bonds with nonparental caretakers. Indeed, “infants nurtured by multiple caretakers grow up not only feeling secure but with better-developed and more enhanced capacities to view the world from multiple perspectives” (p. 132). And in essence, since children with reliable alloparental care would have had access to more calories and care-taking resources, they would have survived better than those who didn’t, thus generating an adaptive selection pressure for the development in infants of the mind-reading capacities necessary to solicit help from others.

The fifth chapter takes on standard evolutionary theories of parental investment and considers the potential role of fathers in successful childrearing. A standard story might be that because females rely on the assistance and resources of fathers to raise their children, the practice of pair-bonded monogamy arose due to a tacit “sex contract” between males and females. In essence, the contract states that in return for parental investment, the females will “exclusively” offer the male sexual access. But Hrdy wonders what happens when the “loving father” is not around to help? Could alloparents step in? In light of paleoanthropological data concerning the relative infrequency of male hunters scoring meat in the Pleistocene, as well as numerous anthropological data describing the strong egalitarianism of hunter-gatherer tribes (sharing the spoils of the hunt with nonkin during large communal feasts), Hrdy says “It’s clear that the most successful hunter would often get no more for his family than the most hapless did” (p. 149).  Here Hrdy approvingly cites Kristen Hawkes’  “show-off hypothesis” (1991) where the benefit of successful male hunting was cashed out more in terms of prestige and reputation rather than pure caloric load distributed to kin. Accordingly, it is the hard work of female gatherers that probably made the biggest daily caloric impact on the survival of children. And if such females could form matrilinear coalitions for cooperative breeding, an inflexible sex contract to secure caretaking resources would have been unnecessary,  leaving room for more flexible parenting (and mating) strategies, including ones where the males don’t offer care exclusively to their kin (which is not to say fathers would place equal weight on nonkin, see p. 157)

As Hrdy puts it, “At the heart of the [sex contract] model lay a pact between a hunter who provided for his mate and a mate who repaid him with sexual fidelity so the provider could be certain that children he invested in carried at least half of his genes” (p. 147). Hrdy doesn’t deny the existence of sexual jealously and male concerns about paternity, but Hrdy’s moral is that “A fixation with genetic paternity obscures the full range of emotions and motives that influence nurturing tendencies in men, and may also obscure their impacts on child survival” (p. 159). Such strategic flexibility might explain the existence of otherwise puzzling cultural diversity concerning male sexual proprietariness, including so-called “partible-paternity” societies like the Eskimos, Montagnais-Naskapi, Central American people like the Siriono, and many tribes in Amazonian South America (p. 153).

Hrdy spends the rest of the book bringing more empirical data to the table and elaborating on the theory of alloparenting, including further analyzing the conditions that favor alloparenting in other species (chapter six), the features of babies that makes them so alluring (“sensory traps”) to adult caretakers (chapter seven), the importance of grandmothers in hunter-gatherer societies (“the most reliably beneficial of all alloparents” (p. 260)) and how this might have facilitated matrilocal (or “matri-patrilocal”) rather than strictly patrilocal residence patterns in the EEA (chapter eight), and finally,  a consideration of various life history traits such as long childhood and as well as some broad and speculative thoughts about how the rise of agrarian civilization affected female sexual autonomy (chapter nine).

To appreciate the significance of Hrdy’s scholarship, it helps to review a standard methodological procedure for doing evolutionary psychology. First, you identity an adaptive problem facing our ancestors in the EEA e.g. the problem of finding a good mate. Second, you develop a computational model that is capable of solving this problem e.g. gather evidence about proxies of fitness such as facial symmetry. Third, you hypothesize plausible neurological mechanisms that could realize the computational solution. Last, you run experimental tests looking for confirmation that the hypothesized mechanisms actually exist. Crucially, this methodology will only produce plausible results if you can realistically set up the initial adaptive problem. That is, if your assumptions about the problems encountered in the EEA are mistaken, then the rest of your explanation will inherit the mistake and you will end up proposing solutions to a problem that never existed. Accordingly, the success of evolutionary psychology as a discipline critically depends on using all of the scant evidence available to make realistic assumptions about the EEA.

Some standard assumptions about the EEA are unassailably right e.g. female pregnancy. But other standard assumptions about possible parenting investment strategies are more questionable. For example, I already mentioned the standard “sex contract” account whereby females “agree” to stop sleeping around with other men in order to secure their fatherly resources. This tense arrangement supposedly benefits both parties. The men receive assurance that they won’t waste resources on some other man’s baby, and the women receive assurance that they will have enough resources from a committed male to raise their baby. This story is supposed to take us all the way from the Pleistocene to contemporary cultural patterns of serial monogamy (albeit with occasional but limited cheating). However, several recent books  (Barash & Lipton, 2001; Ryan & Jethá, 2010)[3] have challenged the standard sex contract story on several dimensions (particularly the assumption that females actually are sexually monogamous). The most relevant dimension for our purposes is skepticism about the following assumption:  the strategy of a father providing care to anyone outside his direct kin network is not evolutionarily stable due to the pressure of competing “selfish” fathers who only provide care to their kin. In a critical review of the latter book, Ellsworth (2011) attempts to undermine the alternative narrative by approvingly citing Thornhill and Gangestad (2008) in claiming the “primary selective pressures favoring such female estrus adaptations were pair-bonding and dependence on male provisioning” (p. 332, emphasis added). However, if Hrdy’s emphasis on the importance of alloparental care for decreasing childhood mortality rates has any validity, then the standard sex contract story needs to be updated to allow for the possibility of more flexible and opportunistic female mating strategies. If alloparental care was available from non-fathers, then mothers would not have depended entirely on male provisioning and could have more room for strategic maneuvering through matrilineal coalitions and extra-pair mating  (Greiling & Buss, 2000).

While many details are needed to flesh out her narrative, Hrdy manages to synthesize a remarkably diverse catalogue of evidence from a variety of academic fields to paint a picture of the human species that tentatively answers the question: Why us and not them? The field of evolutionary psychology has long been accused of telling groundless “Just so stories” that miss the complexity of human life, but Hrdy’s book is a persuasive testament to the sweeping power of informed evolutionary explanation. Hrdy weaves decades of interdisciplinary research into a compelling and charmingly human story, one that challenges the necessity of overly Machiavellian or “demonic” metaphors[4] when describing the whole of our prosocial life, particularly when it comes to understanding the emotions that regulate the critical mother-child relationship. If nothing else, Mothers and Others paints a tantalizing portrait of what 21st evolutionary psychology might look like, and for that, Hrdy should be commended.


Barash, D., & Lipton, J. (2001). The Myth of Monogamy: Fidelity and Infidelity in Animals and People. New York: W.H. Freeman and Company.

Choi, J. K., & Bowles, S. (2007). The coevolution of parochial altruism and war. science, 318(5850), 636-640.

Ellsworth, R. (2011). The Human That Never Evolved. Evolutionary Psychology, 9(3), 325-355.

Greiling, H., & Buss, D. M. (2000). Women’s sexual strategies: The hidden dimension of extra-pair mating. Personality and Individual Differences, 28(5), 929-963.

Hawkes, K. (1991). Showing off: tests of an hypothesis about men’s foraging goals. Ethology and Sociobiology, 12(1), 29-54.

Herrmann, E., Call, J., Hernandez-Lloreda, M. V., Hare, B., & Tomasello, M. (2007). Humans Have Evolved Specialized Skills of Social Cognition: The Cultural Intelligence Hypothesis. Science, 317(5843), 1360-1366.

Hrdy, S. (2009). Mothers and Others: The Evolutionary Origins of Mutual Understanding. Cambridge, MA: Harvard University Press.

Ryan, C., & Jethá, C. (2010). Sex at dawn: The prehistoric origins of modern sexuality. New York: Harper.

Thornhill, R., & Gangestad, S. W. (2008). The evolutionary biology of human female sexuality. New York: Oxford University Press.

Tomasello, M. (1999). The Cultural Origins of Human Cognition. Cambridge, MA: Harvard University Press.

Wrangham, R., & Peterson, D. (1996). Demonic Males: Apes and the Origins of Human Violence. Boston: Houghton Mifflin.


[1] Hrdy claims that despite abundant evidence for intergroup conflict within the past 10-15,000 years, “there is no evidence of warfare in the Pleistocene” (p. 19). Rather, homicidal violence among hunter-gatherers “tend to involve individuals who know each other rather than warfare between adjacent groups” (ibid.).

[2] Hrdy also points out tha “cooperative breeding occurs in a taxonomically diverse array of anthropod, avian, and mammalian species, including some 9 percent of roughly 10,000 species of birds and at least 3 percent of all mammals” (p. 177).

[3] The latter book has a more aggressive and less scholarly tone than the former, but both are challenging similar elements of the standard monogamous sex-contract narrative.

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Book notice: William Calvin's The Cerebral Symphony

William Calvin, otherwise known as “That guy who talks about throwing a lot”, is one of my favorite popularizers of neuroscience. The Cerebral Symphony (1989) is an attempt to explain what it is that makes human consciousness so special. One of my favorite things about Calvin’s approach to human consciousness is that, in his view, “The term should capture something of our advanced abilities rather than covering the commonplace” (p. 78). In other words, the primary explanandum of consciousness studies is not the “sensory qualia” we share with nonhuman animals, but rather, our ability for abstract thought, imagination, and “mental time travel”. That is, Calvin is trying to explain the more “narratological” aspects of consciousness (to borrow a term from Julian Jaynes, who Calvin cites approvingly on this issue) as opposed to the more sensorimotor aspects. However, being a Darwinian, Calvin doesn’t want to necessarily say that capacities that make humans able to narrate and imagine sprung out of evolutionary thin air, so perhaps there are some functional overlaps with other primate species.

The central explanatory tool of the book is what Calvin calls a “Darwin Machine”, which is a variant of the “neural darwinism” approach to brain function. Calvin’s idea goes something like this: suppose the evolution of the ability of humans to throw (and thus hunt more efficiently) necessitated the development of a “neural sequencer” that plans linear motor patterns. Now imagine you have a massive array of sequencers operating in parallel but generating different “variations on a theme”. Calvin’s idea is that consciousness is the sequence that best survives based on various selection criteria that change depending on the task at hand. This is in fact very similar to Dennett’s notion of “multiple drafts” or “fame in the brain”, and I think I first heard of Calvin’s book in Dennett’s 1991 book Consciousness Explained. To me it sounds like pretty much the same theory, which limits the originality of Dennett’s theoretical framework (supposing that Calvin came up with the idea first). Overall, The Cerebral Symphony is an interesting and theoretically insightful account of human consciousness that is solidly grounded in Darwinian thinking (perhaps to a fault). The book is also interspersed with sociological commentary on the scientific community at Woods Hole in Cape Cod Massachusetts, which makes for relatively easy reading.

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